This invention relates to the field of surveillance systems, and in particular to a video surveillance system that includes blocking zones to reduce false alarms.
Video surveillance systems are commonly used to detect intruders in protected areas and/or to track objects that traverse protected areas. Generally, video images are processed to identify objects of interest, and to notify an operator of the system of any unauthorized ventures in the protected area. To facilitate an analysis of the potential unauthorized entry (forensics), the path of the object before and after the entry is provided to the operator.
Exclusion zones are commonly used in video surveillance systems to mask regions of the video image that should not be recorded for privacy reasons (see, for example, U.S. Pat. No. 6,509,926, “SURVEILLANCE APPARATUS FOR CAMERA SURVEILLANCE SYSTEM”, issued 21 Jan. 2003 to Mills et al., and incorporated by reference herein), or to mask regions that trigger false alarms due to motion of trees, reflections, and so on (see, for example, U.S. Pat. No. 5,956,424, “LOW FALSE ALARM RATE DETECTION FOR A VIDEO IMAGE PROCESSING BASED SECURITY ALARM SYSTEM”, issued 21 Sep. 1999 to Wootton et al., and incorporated by reference herein; see also U.S. Pat. No. 6,069,655, “ADVANCED VIDEO SECURITY SYSTEM”, issued 30 May 2000 to Seeley et al., and incorporated by reference herein).
A problem with conventional exclusion regions is that the video image within the region is masked, so that any and all activity within the region is indiscriminately blocked from view and/or analysis. A user may use an exclusion region to mask a cluster of trees, to prevent false alarms caused by motion of the trees, but if a person or automobile travels in front of these trees, their motion will also be masked from generating an alarm.
FIGS. 1A and 1B illustrate example camera views from a video surveillance system.
In FIG. 1A, the area in front of an entrance 120 to a secured building 110 is monitored. The example area includes trees 130. In a conventional surveillance system, one or more exclusion regions would typically be defined to mask the trees 130, so that movements of the leaves or branches of the trees 130 are not tagged as reportable events. Such masking, however, will also mask the movement of a person 140 in the vicinity of the trees 130, thereby producing a potential security gap in the surveillance of the area.
In FIG. 1B, a section of a room is monitored. The room includes a doorway 160, and a mirror 150. When the door is open, any activity in the hallway is visible, including, for example, a person 170 walking by the door. In a conventional surveillance system, an exclusion zone may be defined to mask the activity at the doorway 160, but in so doing, the recognition of a person entering the room is delayed until the person is beyond the masked area. In like manner, an exclusion zone will typically be defined to cover all mirrors or windows, to mask reflections of a person 180 at the opposite end of the room, or persons beyond the secured premises. If a person walks in front of the masked mirror 150, however, a substantial amount of the person's image will be masked, and object-detecting algorithms may fail to identify the remainder image as a trackable object.
An object of this invention is to provide a scheme that facilitates the advantages provided by exclusion zones without incurring their inherent disadvantages. Another object of this invention is to provide a continuous record of an object's travel for forensic purposes.
These objects, and others, are achieved by a method and system that employs blocking zones that are configured to prevent false alarms caused by motion within the zones, but also allow the tracking of objects through the zones. An object that first appears within a blocking zone is not considered to be a reportable object until the object leaves the zone. All reportable objects are tracked, without regard to the blocking zones. Objects that remain within their initial blocking zone are not deemed to be reportable objects, and therefore do not generate alarms. If an object initially appears within overlapping zones, the object is not deemed to be reportable until it leaves each of the zones at least once. The blocking zones do not mask the video images, and thus a complete record of activity is available for forensic purposes.
Throughout the drawings, the same reference numerals indicate similar or corresponding features or functions. The drawings are included for illustrative purposes and are not intended to limit the scope of the invention.